1. Technical Field
This invention relates to energy absorbing guard rail terminals of the type which are used along the roadside and in the median between limited access highways to deflect vehicles from hazards which can be associated behind the barriers. Guard rails are typically defined of a W-shaped configuration mounted on a plurality of spaced posts so as to function primarily in tension when redirecting the impact of the vehicles.
2. Description of Prior Art
Prior Art devices of this type have relied on a variety of different structural configurations design to redirect, reflect and to absorb the kinetic energy of the vehicle upon impact, see for example U.S. Pat. No. 4,655,434, U.S. Pat. No. 4,452,431, U.S. Pat. No. 4,678,166 and U.S. Pat. No. 4,330,106.
In U.S. Pat. No. 4,655,434 an absorbing guard rail terminal is disclosed in which applicant's invention is an improvement thereon.
In U.S. Pat. No. 4,452,431 a restorable fender panel is disclosed wherein a reusable impact attenuation device is provided to collapse under the impact of a vehicle in protecting stationery structures from damage.
Buffer elements are interposed between the diaphram panel members, thus absorbing the kinetic energy of the vehicle as the successive buffer elements are compressed therebetween.
In U.S. Pat. No. 4,678,166 an eccentric loader guard rail terminal is disclosed for use at the upstream end of a conventional guard rail utilizing a plurality of joined together horizontally extending W-beam guard rails. The device is devised so as to utilize an eccentric lever means whereby as the impacting vehicle at the upstream end will facilitate buckling of the rails allowing the vehicle to pass behind the terminal preventing possible roll over or other destabilizing features associated with vehicle impact on a barrier.
In U.S. Pat. No. 4,330,106 a guard rail construction is disclosed which utilizes a plurality of overlapping guard rail sections with each of the rail elements attached to the adjoining or overlapping section by a bolt so that upon actual impact the rail sections will move axially with respect to one another, but remain in full tensile strength and thus maintaining their redirectional characteristics.
Development of terminal designs is complicated by the need to minimize resistance for small car impacts while still providing the necessary strength for full size car impacts either on the end or downstream of the approach end.
The present invention is directed to improvements to an energy absorbing guard rail terminal which functions essentially as a crash cushion providing a series of spaced opening which are in line with splice bolts when two beams are overlapped. This provides an energy absorbing mechanism as the rails are telescoped relative to each other by the splice bolts shredding out the metal strips between the openings. The shredding of the material provides a uniform and controlled energy absorbtion mechanism. In addition the sections of the guard rails are staggered so that the upstream section will telescope first so as to minimize resistance for the small car impacts while still providing strength necessary to absorb full size car impacts.